In a scanned beam display or the like, a touch or input may be detected via introducing passive interference, for example using a reflector or retroreflector in the projection cone or on the projection surface. The interference may be detected by appropriate circuitry and decoded to correspond to the physical location of the input devices in a two-dimensional plane with respect to the projected image as X-Y coordinates. The detected interference may then be indicated as a pointer event or a touch event to a video rendering engine to overlay the position of the input device in the projected image or to actuate an event, for example via gesturing. When multiple input devices are utilized, the position of the respective input devices may be determined. However, when the input devices cross over an imaginary horizontal line any where in the scanned region, the ability to accurately track the individual input devices may be lost or their coordinates inadvertently may be swapped, and as a result the wrong X-Y coordinates may be associated with the wrong input device.
The reason such “swapping” might happen is due to the nature by which the coordinates of the input devices are detected, tagged to or associated with an input device, and passed along to the application layer. This tagging occurs in the time domain, and temporal separation between the input devices is what yields a unique tag. However, when the input device violates this temporal relationship if the relative positions of the input devices along the raster scan are swapped, then their tags will also be inadvertently swapped. Thus, detection and correction of such temporal violations should be accounted for in order to maintain the integrity of the tags with a corresponding input device.
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